1. Field of the Invention
The present invention is broadly concerned with pelletized finely divided adsorbents selected from the group consisting of metal oxides, metal hydroxides, and mixtures thereof, and methods of forming such pellets. The pellets are preferably formed by pressing the finely divided metal adsorbents at pressures of from about 50 psi to about 6000 psi to yield self-sustaining bodies which retain at least about 25% of the surface area/unit mass and total pore volume of the starting metal adsorbents prior to pressing thereof. In use, target compound(s) are contacted with adsorbent pellets of the invention to destructively adsorb or chemisorb the target compound(s).
2. Description of the Prior Art
There is mounting concern about air quality, particularly the quality of indoor air. In most cases, indoor air is of worse quality than outdoor air. The removal of gaseous contaminants from air can be achieved by the application of a variety of principles. These include adsorption, catalytic transformation, and absorption. Among these adsorption is the most widely applied method. In adsorption, gases, vapors, or liquids come into contact with the surface of the adsorbent and adhere to it to some degree. This adsorption can be the result of residual physical forces (Van der Waal's forces) or chemical binding to the surface where the adsorbed molecule binds stronger to the adsorbing surface. Although adsorption can occur on a variety of solid surfaces, only a few materials have adsorptive characteristics sufficiently favorable for air cleaning. These include activated carbons, zeolites, molecular sieves, silica gel, and activated alumina.
Activated carbon has been the most commonly used in dealing with purification of air. The highest quality activated carbon is made from coconut shells and has a surface area/unit mass of about 600-900 m.sup.2 /g. However, activated carbon does not strongly adsorb air pollutants and the adsorbed material can be released over time with continued air flow. Moreover, activated carbon is difficult to clean up.
Another tool for indoor air purification is an electrostatic filter. Electrostatic filters work well at removing particulates from the indoor air. However, electrostatic filters are inadequate at removing many chemical vapors from the air, and there are numerous chemical vapor air pollutants which are of concern. The most prevalent of these include formaldehyde, acetaldehyde, methanol, methylene chloride, carbon tetrachloride, carbon monoxide, dimethyl amine, toluene, benzene, sulfur dioxide, acetonitrile, nitrosoamine, and nitrogen dioxide.
Nanocrystals make up a high surface area form of matter that can serve as another adsorbent which can be used for removing pollutants such as chlorocarbons, acid gases, military warfare agents, and insecticides from the air. The unique chemical reactivity of nanocrystals allows the destructive adsorption and chemisorption of toxic substances and are a substantial advance in air purification. However, nanocrystals are a very fine dust which take up large volumes of space and are conducive to electrostaticity, thus making them difficult to handle and at times inconvenient.
There is a need for an adsorbent compound capable of strongly adsorbing air pollutants which does not release those pollutants over time. Furthermore, this adsorbent compound must be easy to handle and be of decreased volume compared to nanocrystal adsorbents.